A variety of audio devices, including state of the art mobile telephones, include a primary microphone that is positioned and oriented to receive audio from an intended source, and a reference microphone that is positioned and oriented to receive background noise while receiving little or no audio from the intended source. In many usage scenarios, the reference microphone provides an indicator of the amount of noise that is likely to be present in a primary channel of an audio signal obtained by the primary microphone. In particular, the relative spectral power levels, for a given frequency band, between the primary and reference channel may indicate whether that frequency band is dominated by noise or by signal in the primary channel. The primary channel audio in that frequency band may then be selectively suppressed or enhanced accordingly.
It is the case, however, that the probability of speech (respectively, noise) dominance in the primary channel, considered as a function of the unmodified relative spectral power levels between the primary and reference channels, may vary by frequency bin and may not be stationary over time. Thus the use of a raw power ratios, fixed thresholds, and/or fixed rescaling factors in interchannel comparison-based filtering may well result in undesirable speech suppression and/or noise amplification in the primary channel audio.
Accordingly, improvements are sought in estimating the differences in noise-dominant/speech-dominant power levels between input channels, and in suppressing noise and enhancing speech presence in the primary input channel.